PT-2026-41147 · Pypi · Mistune

Across-Verticals-Malaysia + 1 · Published 2026-05-14 · Updated 2026-05-26 · CVE-2026-44899

Positive Technologies (AI Summary)

CVSS v3.1

4.7

Medium

Base vector

AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N

Name of the Vulnerable Software and Affected Versions mistune (affected versions not specified)

Description The Image directive plugin fails to properly validate the :width: and :height: options. The validation uses a regular expression that only checks if the value starts with a digit, rather than ensuring the entire string is a valid number. When a value is not a plain integer, it is inserted directly into a style attribute without escaping.

This allows an attacker to inject arbitrary CSS properties by providing a value that begins with digits followed by malicious CSS. For example, using the :width: parameter, an attacker can inject properties such as position:fixed, background-color, and z-index to create a full-page phishing overlay or perform UI redressing attacks, effectively covering the entire browser viewport and concealing legitimate page content.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

XSS

Weakness Enumeration

CWE-79

Related Identifiers

CVE-2026-44899

GHSA-CCFX-MFMX-2FX9

Affected Products

Mistune

References · 6

• https://nvd.nist.gov/vuln/detail/CVE-2026-44899 · Security Note
• https://osv.dev/vulnerability/GHSA-ccfx-mfmx-2fx9 · Vendor Advisory
• https://github.com/lepture/mistune/releases/tag/v3.2.1 · Note
• https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9 · Note
• https://github.com/lepture/mistune · Note
• https://twitter.com/dailycve/status/2055005658412458117 · Twitter Post